Personalized 100 Days Of School 100 Days of Cool T-Shirt. This Happy 100 days of school design is the perfect outfit for kids looking to celebrate their 100th day of school in style. With its cute design, it is sure to make your little one stand out. Whether it's for a boy or a girl, this outfit is a great choice. Wardrobe essential for looking good, 24/7. 5.0 oz., pre-shrunk 100% cotton. Seamless 1x1 rib collar. Shoulder-to-shoulder taping. Double-needle stitched sleeves, bottom hem and front neck. Note: greys are a cotton/polyester blend.